The present invention relates to a stop valve. An example of the conventional stop valve is disclosed in Japanese Utility Model Publication No. 28151/61 and is shown in FIG. 3. According to this conventional structure, a valve seat 3' is positioned within a fluid path formed in a main body 1'. The valve seat 3' confronts a valve body 4' disposed at a lower end of a valve rod (spindle) 6'. The valve rod 6' is centrally disposed within a cap member 2' and is threadingly engaged therewith. The cap member 2' is disposed above the main body 1' and is engaged therewith. Upon rotation of a handle 16' connected to an upper end of the valve rod 6', the valve rod 6' moves along its axial direction within the cap member 2', to thereby control the degree of opening of the valve body 4' relative to the valve seat 3'. Further, a gland chamber is provided at the upper half inner portion of the cap member 2' so as to surround the valve rod 6'. Within the hollow gland chamber, a packing receiver 8', a gland packing 10' and a packing holder 9' are successively fitted.
With this structure, direct rotational sliding contact is made between the gland packing 10' and the valve rod 6', since the valve rod 6' not only rotates but also moves along its axial direction. Therefore, during operation, the gland packing 10' is subject to frictional force along both the circumferential and axial directions of the valve rod 6', so that the packing is excessively worn. The amount of wear is disadvantageously increased due to both the rotational and axial movement of the valve rod 6' and, due to the repetition of the operations, the packing must be often replaced with a new one. Further, since liquid may be introduced into the threadingly engaging portion between the valve rod 6' and the cap member 2', foreign materials may be accumulated thereon and corrosion may result, to thus lower the efficiency of the stop valve. Such a disadvantage may become most apparent when a liquid such as slurry flows through the stop valve.
Another type of the conventional stop valve is disclosed in Japanese Industrial Standard (JIS) No. B 2041. This publication discloses a flanged globe valve which is referred to as an external thread type. According to this stop valve, a yoke member forming a thread adapted to provide vertical movement of a valve rod is provided. Since the yoke is positioned above a cap member, the thread portion is free from liquid contact. However, a packing is employed in the device which therefore still suffers from the disadvantages mentioned above in connections with the first conventional device.